While it is not exactly about mixing liquids, it involves pouring liquids alright.
You have three containers whose capacity are 12 gallons, 8 gallons and 5 gallons respectively. The 12 gallon container is filled with water and the other two are empty. You have nothing else. You have to divide the water into two parts of 6 gallons each. In other words, by a sequence of pouring from one container to the other, you have to eventually have 6 gallons in the 12 gallon container and another 6 gallons in the 8 gallon container.
How would you do it?